Apparatus and methods for the continuous polymerization of water soluble polymers are the subject matter of a number of U.S. patents. Thus, U.S. Pat. No. 2,820,777 discloses a continuous process for polymerizing and hydrolyzing acrylamide. The patent contains no teaching with regard to apparatus for carrying out the process. U.S. Pat. No. 3,732,193 discloses a continuous polymerization process in which an aqueous solution of a water soluble unsaturated monomer such as acrylamide is polymerized on a heated, continuously moving belt to produce a polymer in a dry, thin film form. In U.S. Pat. No. 4,110,521 there is disclosed apparatus for the continuous polymerization of water soluble polymers. The apparatus comprises a jacketed, tubular reactor which contains static mixers, a jacketed post reactor, also containing static mixers, and a diluter containing static mixers for mixing the polymer and water feeds. A jacketed tank is provided for retaining reactants to be added to the post reactor. According to the patent, the end product from the diluter can go to bulk storage or it may be used directly.
The apparatus disclosed in U.S. Pat. No. 3,732,193 would, for all practical purposes, be useless for the on-site preparation of aqueous polymer solutions of the type employed in the secondary and tertiary recovery of oil from subterranean oil-bearing formations. The apparatus shown in U.S. Pat. No. 4,110,521, while having obvious advantages over the apparatus of U.S. Pat. No. 3,732,193 for the preparation of aqueous polymer solutions for use in secondary and tertiary oil recovery operations, has a number of shortcomings which detract from its adaptation for the on-site preparation of such solutions. More specifically in this connection, the apparatus of the patent is characterized by its extensive use of static mixers. Static mixers are costly and their use on the scale contemplated in the patent would make the apparatus prohibitively expensive. In addition, the apparatus of the patent requires the use of temperature control jackets not only on the reactors, but, also, on each of thc tanks or vessels used for the reactants. The use of cooling or heating jackets of the size and type contemplated in the patent further adds to the complexity and to the cost of the apparatus. Yet another significant shortcoming of the apparatus of the patent, and one to which no reference is made in the patent, concerns the properties of the polymer solutions prepared with the apparatus. Thus, while the patent has for one of its objects the provision of apparatus in which the reaction conditions are controlled to produce polymers of uniform molecular weight and molecular weight distribution, it does not disclose means for preparing polymer solutions in a manner to prevent, or reduce to minimum levels, degradation of the polymer comprising the solutions. Degradation, or thinning, of the polymer adversely affects the injectivity and mobility properties of the polymer solution thereby lessening to an appreciable degree its ability to satisfy the performance demands of an oil-bearing formation.